CN114865225A - Composite diaphragm, preparation method thereof and lithium ion battery - Google Patents

Composite diaphragm, preparation method thereof and lithium ion battery Download PDF

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Publication number
CN114865225A
CN114865225A CN202210345179.9A CN202210345179A CN114865225A CN 114865225 A CN114865225 A CN 114865225A CN 202210345179 A CN202210345179 A CN 202210345179A CN 114865225 A CN114865225 A CN 114865225A
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Prior art keywords
coating
mixed
aramid fiber
composite
slurry
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黄佳苑
黎中利
冀亚娟
赵林燕
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Eve Energy Co Ltd
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Eve Energy Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/423—Polyamide resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/431—Inorganic material
    • H01M50/434—Ceramics
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/44—Fibrous material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/443—Particulate material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491—Porosity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/494—Tensile strength
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Inorganic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Ceramic Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Composite Materials (AREA)
  • Cell Separators (AREA)

Abstract

The invention provides a composite diaphragm, a preparation method thereof and a lithium ion battery. The composite diaphragm comprises a polyimide base film and a mixed coating at least coated on one side of the polyimide base film; the mixed coating comprises the following components in percentage by mass: 80-85% of ceramic particles, 5-12% of aramid fiber, 2-4% of binder, 0.5-1% of dispersant, 0.5-2.5% of thickening agent and 0.1-1% of wetting agent. The composite diaphragm provided by the invention adopts a specific component formula, a small amount of doped aramid fiber and a dot coating mode, can greatly reduce the cost and realize simple large-scale production, and can improve the tensile strength, the ductility, the electrolyte liquid retention capacity and the puncture resistance of the diaphragm, and has higher porosity and lower air permeability.

Description

Composite diaphragm, preparation method thereof and lithium ion battery
Technical Field
The invention belongs to the technical field of diaphragm materials, and particularly relates to a composite diaphragm, a preparation method of the composite diaphragm and a lithium ion battery.
Background
The diaphragm is used as an important component of the lithium ion battery, mainly plays a role in isolating the positive electrode and the negative electrode, has ion insulation property and only transmits electrons. In order to further improve the high-temperature cycle performance of the battery, many researchers have applied a high-temperature resistant coating on the surface of the separator to improve the thermal stability of the separator.
CN109411676A discloses a para-aramid coating slurry and a preparation method thereof, a para-aramid diaphragm and a preparation method thereof and a secondary battery, wherein the para-aramid coating slurry comprises a solution A and a solution B in a mass ratio of (6-2) to 1; the solution A comprises 65-85 parts of para-aramid dissolving solution and 10-20 parts of non-solvent by weight; the solution B comprises 40-55 parts of a first solvent, 0.5-2 parts of a dispersing agent and 45-60 parts of inorganic particles. The heat-resistant composite membrane has the characteristics of enhanced thermal stability, increased mechanical strength and the like, improves the heat-resistant stability and heat-resistant shrinkage rate of the membrane, but has thicker thickness and poorer air permeability, and simultaneously has complicated preparation process.
However, the current thermal pore-closing coating diaphragm still has the problems of thick thickness, poor heat-resistant stability and poor mechanical property, and is easy to be pierced by lithium dendrite, which is not favorable for further improving the safety performance and electrochemical performance of the lithium ion battery, so that it is necessary to develop a high-temperature-resistant and puncture-resistant composite diaphragm.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a composite diaphragm, a preparation method thereof and a lithium ion battery. The composite diaphragm provided by the invention adopts a specific component formula, a small amount of doped aramid fiber and a dot coating mode, so that the cost can be greatly reduced, the simple large-scale production can be realized, the tensile strength, the ductility, the electrolyte liquid retention capacity and the puncture resistance of the diaphragm can be improved, and the diaphragm has higher porosity and lower air permeability; even can not catch fire through the acupuncture test, effectively improve the security and the life-span of diaphragm and battery to can apply in the battery of power automobile and lithium ion battery field in a large number, thereby realize the purpose that the battery charges and discharges with big multiplying power, and improved multiplying power performance, cycle life, heat-resisting stability and the security performance of battery.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a composite separator, including a polyimide base film and a hybrid coating layer at least coated on one side of the polyimide base film;
the mixed coating comprises the following components in percentage by mass: 80-85% of ceramic particles, 5-12% of aramid fiber, 2-4% of binder, 0.5-1% of dispersant, 0.5-2.5% of thickening agent and 0.1-1% of wetting agent.
In the present invention, the mass percentage of the ceramic particles in the mixed coating is 80% to 85%, and may be, for example, 80%, 81%, 82%, 83%, 84%, 85%.
In the invention, by adjusting the mass percentage of the ceramic particles in the mixed coating, the air permeability, the ionic conductivity and the heat-resistant shrinkage rate of the coating film are better, if the content is too low, the air permeability and the heat-resistant shrinkage rate of the coating film are reduced, and if the content is too high, the surface density of the coating film is higher, so that the improvement of the performance of the battery is not facilitated.
In the present invention, the mass percentage of the aramid fiber in the hybrid coating layer is 5% to 12%, and may be, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%.
In the invention, the mass percentage of the aramid fiber in the mixed coating is adjusted, so that the coating film achieves high heat resistance and low cost, the heat resistance of the diaphragm is poor when the content is too low, and the cost is too high when the content is too high.
In the present invention, the content of the binder in the hybrid coating layer may be 2% to 4% by mass, for example, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.2%, 3.5%, 3.7%, 4%.
In the invention, the mass percentage of the binder in the mixed coating is adjusted to make the binding power and the air permeability of the coating film better, wherein the too low content can result in the too low peel strength of the coating film, and the too high content can reduce the air permeability of the coating film and is not beneficial to improving the electrical property.
In the present invention, the content of the dispersant in the mixed coating layer may be 0.5% to 1% by mass, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.
In the invention, the mass percentage of the dispersing agent in the mixed coating is adjusted, so that the air permeability and the thickness consistency of the coating film are better, the components are difficult to disperse due to too low content, the agglomeration phenomenon is caused, the thickness and the air permeability consistency of the coating film are poor, and the air permeability of the coating film is reduced and the electrical property is not favorably improved due to too high content.
In the present invention, the content of the thickener in the mixed coating layer may be 0.5% to 2.5% by mass, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.5%.
In the invention, the mass percentage of the thickening agent in the mixed coating is adjusted, so that the coating slurry property of the coating film is more stable and the consistency of the coating film is better, the precipitation phenomenon of the coating slurry is easy to occur and the consistency of the coating film is poor when the content is too low, and the coating process is difficult to implement when the content is too high.
In the present invention, the content of the wetting agent in the mixed coating layer may be 0.1% to 1% by mass, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%.
In the invention, by adjusting the mass percentage of the wetting agent in the mixed coating, the coating slurry of the coating film is more easily attached to the surface of the diaphragm and is not easy to fall off, the wettability of the diaphragm and the permeability of the coating are favorably improved, the coating cannot be attached to the surface of the diaphragm when the content is too low, and the ionic conductivity and the electrical property of the coating film are favorably improved when the content is too high.
According to the invention, the combination of three high-temperature resistant materials, namely the polyimide base film, the ceramic particles and the aramid fiber with specific contents is adopted, so that the high-temperature resistance of the diaphragm is greatly improved, the ion transmission can be quickly cut off at a high temperature, the battery reaction is interrupted, the battery temperature is prevented from continuously rising, and the occurrence of thermal runaway is effectively prevented; meanwhile, the adhesive, the dispersing agent, the thickening agent and the wetting agent are matched with each other, so that the adhesive, the dispersing agent, the thickening agent and the wetting agent have good tensile mechanical property, higher extensibility, puncture resistance, high temperature resistance and flame retardant effect, and the phenomenon that the battery does not catch fire through extrusion and needling tests and the bad burr result caused by winding and trimming of the battery can be avoided.
Preferably, the thickness of the composite separator is 9 μm to 13 μm, and may be, for example, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm.
Preferably, the porosity of the composite separator is 44% to 46%, for example, 44%, 45%, 46% may be provided.
According to the invention, the composite diaphragm has good air permeability and low ionic conductivity by adjusting the thickness and porosity of the composite diaphragm.
Preferably, the thickness of the hybrid coating is 4 μm to 6 μm, and may be, for example, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm.
In the invention, the thickness of the mixed coating is adjusted to enable the coating film to have more excellent heat resistance and air permeability, and if the thickness is too thin, the heat resistance of the diaphragm is poor, otherwise, the air permeability of the diaphragm is poor.
Preferably, the thickness of the polyimide-based film is 5 μm to 7 μm, and may be, for example, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm, 6.2 μm, 6.5 μm, 6.8 μm, 7 μm.
Preferably, the polyimide-based film has a porosity of 55% to 65%, for example 55%, 57%, 59%, 60%, 62%, 65%.
In the invention, the polyimide base film has better mechanical property, is beneficial to improving the puncture resistance of the diaphragm, and simultaneously, the higher porosity of the polyimide base film increases the ionic conductivity of the diaphragm, thereby being beneficial to improving the rate capability of the battery.
In the present invention, the polyimide-based film has a melting point of 250-350 ℃, for example, 250 ℃, 270 ℃, 300 ℃, 320 ℃, 350 ℃.
Preferably, the ceramic particles in the hybrid coating comprise at least one of alumina, boehmite, or silica.
Preferably, the average particle size of the ceramic particles in the hybrid coating is 0.5-1.5 μm, and may be, for example, 0.5 μm, 0.7 μm, 1.0 μm, 1.2 μm, 1.5 μm.
In the invention, the average particle size of the ceramic particles is adjusted, so that the air permeability of the coating film is better, and the porosity and the ionic conductivity are higher.
Preferably, the specific surface area of the ceramic particles in the mixed coating is 6.5-8.9m 2 Per g, for example, may be 6.5m 2 /g、6.7m 2 /g、7.0m 2 /g、7.2m 2 /g、7.5m 2 /g、7.7m 2 /g、8.0m 2 /g、8.2m 2 /g、8.5m 2 /g、8.9m 2 /g。
In the invention, the electrolyte wettability of the coating film is better by adjusting the specific surface area of the ceramic particles, which is beneficial to improving the ionic conductivity and the rate capability.
Preferably, the aramid in the hybrid coating comprises at least one of meta-aramid or para-aramid.
Preferably, the average particle size of the aramid in the hybrid coating is 0.05-0.3 μm, and may be, for example, 0.05 μm, 0.08 μm, 0.1 μm, 0.12 μm, 0.15 μm, 0.17 μm, 0.2 μm, 0.22 μm, 0.25 μm, 0.27 μm, 0.3 μm.
In the invention, the average particle size of the aramid fiber is adjusted, so that the heat resistance and the air permeability of the coating film are better.
Preferably, the glass transition temperature of the aramid fiber in the aramid fiber coating is 400-.
In the invention, the glass transition temperature of the aramid fiber in the mixed coating is adjusted, so that the heat resistance of the coating film is better, the heat resistance of the diaphragm is poor when the temperature is too low, and the heat resistance of the diaphragm is better when the temperature is too high. Preferably, the binder in the mixed coating is polymethyl methacrylate.
In the invention, by selecting the specific polymethyl methacrylate binder, the separator has the advantages of light weight, low price and contribution to improving the tensile and impact resistance of the separator, and is compounded with a dispersing agent, a thickening agent and a wetting agent for use, so that the affinity of the separator and an electrolyte is improved, and the performance of a battery is promoted.
Preferably, the density of the polymethyl methacrylate is 1.1 to 1.3g/cm 3 For example, it may be 1.1g/cm 3 、1.12g/cm 3 、1.15g/cm 3 、1.17g/cm 3 、1.2g/cm 3 、1.22g/cm 3 、1.25g/cm 3 、1.27g/cm 3 、1.3g/cm 3 。
In the invention, the polymethyl methacrylate with a specific density range is selected, so that the bonding strength and the air permeability of the coating film are better.
Preferably, the dispersant in the mixed coating comprises any one or two of sodium tripolyphosphate, sodium hexametaphosphate, triethylhexyl phosphoric acid, sodium dodecyl sulfate, methylpentanol, polyacrylamide or fatty acid polyglycol ester, and is preferably polyacrylamide and/or fatty acid polyglycol ester.
Preferably, the thickener in the mixed coating comprises any one or two of arabic gum, sodium carboxymethyl cellulose, propylene glycol alginate, methylcellulose, sodium starch phosphate, sodium polyacrylate, polyoxyethylene, polyvinylpyrrolidone, vinyl methyl ether-decadiene copolymer, methyl acrylate-decadiene copolymer or polyurethane, and is preferably sodium carboxymethyl cellulose.
Preferably, the wetting agent in the mixed coating comprises any one or two of polyethylene glycol, tween-80, vaseline, polyether modified siloxane copolymer, waterborne polyurethane, polyoxyethylene octylphenol ether, polyoxyethylene castor oil ether or sodium isethionate, and preferably polyethylene glycol 200 and/or polyether modified siloxane copolymer.
Preferably, the mixed coating also comprises a pH regulator.
Preferably, the pH adjusting agent is sodium hydroxide.
In a second aspect, the present invention provides a method of making the composite separator of the first aspect, the method comprising the steps of:
(1) mixing ceramic particles, a binder, a wetting agent, a thickening agent and a solvent to obtain ceramic slurry;
(2) mixing aramid fiber, a dispersing agent, a binder and a solvent to obtain aramid fiber slurry;
(3) and (3) mixing the ceramic slurry obtained in the step (1) and the aramid slurry obtained in the step (2), adding a pH regulator to obtain a mixed slurry, coating the mixed slurry on at least one side of the base film, and drying to obtain the composite diaphragm.
Preferably, the solvent in step (1) is deionized water.
Preferably, the mixing in step (1) is carried out under milling and stirring.
Preferably, the rotation speed of the grinding is 500-1500rpm, for example, 500rpm, 800rpm, 1000rpm, 1100rpm, 1200rpm, 1300rpm, 1400rpm, 1500rpm can be mentioned.
Preferably, the stirring time is 4-15h, for example, 4h, 6h, 8h, 10h, 12h, 15 h.
Preferably, the solvent in step (2) is deionized water.
Preferably, the mixing in step (2) is carried out under milling.
Preferably, the grinding time is 4-15h, for example, 4h, 6h, 8h, 10h, 12h, 15 h.
Preferably, the solid content of the mixed slurry in the step (3) is 35-40%, for example, 35%, 36%, 37%, 38%, 39%, 40% can be realized.
Preferably, the viscosity of the mixed slurry in the step (3) is 50-200cp, for example, 50cp, 70cp, 90cp, 100cp, 120cp, 150cp, 170cp and 200 cp.
Preferably, the coating in step (3) is spot coating.
According to the invention, the dot coating mode is adopted to enable the coating to be more uniform, and meanwhile, the coating diaphragm has the advantages of better thickness and air permeability consistency, the wettability of electrolyte on the isolation diaphragm can be effectively improved, the electrolyte retention amount of the electrolyte is improved, the performance of the battery is further improved, in addition, the water jumping phenomenon in the later cycle period of the battery can be effectively prevented, the aging standing time of the electrolyte is shortened, and the yield and the quality of the battery product are improved.
In a third aspect, the invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm, wherein the diaphragm is the composite diaphragm according to the first aspect.
The composite diaphragm provided by the invention can realize high-rate charge and discharge of the lithium ion battery, and can improve the rate performance, cycle life, heat-resistant stability and safety of the battery.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a composite diaphragm, which adopts ceramic particles, aramid fibers, a binder, a dispersant, a thickener and a wetting agent with specific contents, and the components are matched with each other, so that the following properties of the diaphragm are improved:
(1) the invention effectively improves the wettability of the diaphragm to the electrolyte, improves the liquid retaining amount of the electrolyte, further improves the wettability of the battery, can also effectively prevent the electric quantity water jump phenomenon at the later cycle stage of the battery, shortens the aging standing time of the injected liquid, and improves the yield and the quality of the battery product;
(2) the diaphragm provided by the invention has good tensile mechanical property, higher extensibility, puncture resistance, high temperature resistance and flame retardant effect, can not catch fire and can be subjected to thermal shrinkage test through extrusion and needling tests, and can prevent the bad burr result caused by winding and trimming of the battery;
(3) the invention has the advantages of simple large-scale realization, high quality and low cost production, and the thin thickness (9-13 mu m), low coating surface density, higher porosity (44-46%) and lower air permeability (less than or equal to 260s/100ml), can be widely applied to power automobile batteries and lithium ion batteries, realizes the purpose of high-rate charge and discharge of the batteries, and simultaneously improves the rate capability, cycle life, heat-resistant stability and safety performance of the batteries.
Drawings
Fig. 1 is a schematic structural diagram of a composite separator provided in examples 1 to 5, in which 1 is a polyimide-based film and 2 is a hybrid coating layer.
Detailed Description
The technical solution of the present invention is further explained by combining the drawings and the detailed description. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
This example provides a composite separator, as shown in fig. 1, which includes a polyimide-based film (having a thickness of 6 μm, a porosity of 60%, and a melting point of 300 ℃, available from gagchun high-energy polyimide materials ltd) and a hybrid coating layer coated on at least one side of the polyimide-based film. The mixed coating comprises the following components in percentage by mass: 84 percent of alumina, 10.3 percent of meta-aramid and polymethyl methacrylate (the density is 1.2 g/cm) 3 Glass transition temperature 105 ℃, available from wawa chemical group ltd) 3%, dispersant 0.7%, thickener 1.5%, and wetting agent 0.5%. The thickness of the composite diaphragm is 11 μm, the porosity of the composite diaphragm is 45%, the thickness of the mixed coating is 5 μm, and the D of the alumina 50 The particle diameter is 1 μm, the specific surface area is 7.7m 2 The glass transition temperature of the middle aramid fiber of the mixed coating is 450 ℃, and the average grain diameter is 0.15 mu m.
The preparation method comprises the following steps:
(1) mixing alumina, polymethyl methacrylate, and polyethylene glycol 200 wetting agent (molecular weight: 200; density 1.125 g/cm) 3 Purchased from Jinan Xiangfeng Wei industries chemical Co., Ltd.), sodium carboxymethylcellulose thickener (density of 1.65 g/cm) 3 Purchased from zhengzhou hua crystallography ltd)) and deionized water, wherein the grinding rotation speed is 1000rpm, and the stirring time is 10 hours, so as to obtain ceramic slurry;
(2) grinding meta-aramid (model 1313, available from Jiangxi Shuobao New materials science and technology Co., Ltd.), polyacrylamide dispersant (available from Jinan Jiabin chemical Co., Ltd.), polymethyl methacrylate and deionized water for 10 hours to obtain aramid pulp;
(3) and (3) mixing the ceramic slurry obtained in the step (1) and the aramid slurry obtained in the step (2), adding sodium hydroxide to adjust the pH value to obtain a mixed slurry with the solid content of 37%, wherein the viscosity of the mixed slurry is 125cp, coating the mixed slurry on at least one side of the base membrane, and drying to obtain the composite membrane.
Example 2
This example provides a composite separator comprising a polyimide based film (6 μm thick, 60% porosity, 280 ℃ melting point) and a hybrid coating layer coated on at least one side of the polyimide based film. The mixed coating comprises the following components in percentage by mass: 83 percent of alumina, 11.3 percent of meta-aramid and polymethyl methacrylate (the density is 1.2 g/cm) 3 )3 percent of dispersant, 0.7 percent of thickener and 0.5 percent of wetting agent. The thickness of the composite diaphragm is 10 μm, the porosity of the composite diaphragm is 45%, the thickness of the mixed coating is 5 μm, and the D of the alumina 50 The particle diameter is 0.8 μm, the specific surface area is 7.1m 2 The glass transition temperature of the middle aramid fiber of the mixed coating is 420 ℃, and the average grain diameter is 0.1 mu m.
The preparation method comprises the following steps:
(1) grinding and stirring alumina, polymethyl methacrylate, a polyethylene glycol 200 wetting agent, a sodium carboxymethyl cellulose thickener and deionized water, wherein the grinding speed is 1000rpm, and the stirring time is 10 hours, so as to obtain ceramic slurry;
(2) grinding meta-aramid, a polyacrylamide dispersant, polymethyl methacrylate and deionized water for 10 hours to obtain aramid slurry;
(3) and (3) mixing the ceramic slurry obtained in the step (1) and the aramid slurry obtained in the step (2), adding sodium hydroxide to adjust the pH value to obtain a mixed slurry with the solid content of 36%, wherein the viscosity of the mixed slurry is 100cp, coating the mixed slurry on at least one side of the base membrane, and drying to obtain the composite membrane.
Example 3
This example provides a composite separator comprising a polyimide-based film (6 μm thick, 60% porosity, 320 ℃ melting point) and a hybrid coating layer coated on at least one side of the polyimide-based film. The mixed coating comprises the following components in percentage by mass: 82% of alumina, 11.3% of meta-aramid and polymethyl methacrylate (the density is 1.2 g/cm) 3 )4 percent of dispersant, 0.7 percent of thickener and 0.5 percent of wetting agent. The thickness of the composite diaphragm is 12 μm, the porosity of the composite diaphragm is 45%, the thickness of the mixed coating is 5 μm, and the D of the alumina 50 The particle diameter is 1.2 μm, the specific surface area is 8.3m 2 The glass transition temperature of the middle aramid fiber of the mixed coating is 480 ℃, and the average grain diameter is 0.25 mu m.
The preparation method comprises the following steps:
(1) grinding and stirring aluminum oxide, polymethyl methacrylate, polyethylene glycol 200 wetting agent, sodium carboxymethyl cellulose thickener and deionized water, wherein the grinding speed is 1000rpm, and the stirring time is 10 hours, so as to obtain ceramic slurry;
(2) grinding meta-aramid, a polyacrylamide dispersant, polymethyl methacrylate and deionized water for 10 hours to obtain aramid slurry;
(3) and (3) mixing the ceramic slurry obtained in the step (1) and the aramid slurry obtained in the step (2), adding sodium hydroxide to adjust the pH value to obtain mixed slurry with the solid content of 38%, wherein the viscosity of the mixed slurry is 150cp, coating the mixed slurry on at least one side of the base membrane, and drying to obtain the composite diaphragm.
Example 4
This example provides a composite separator comprising a polyimide-based film (thickness 5 μm, porosity 55%, melting point 250 ℃) and a hybrid coating layer coated on at least one side of the polyimide-based film. The mixed coating comprises the following components in percentage by mass: 80% of alumina, 12% of meta-aramid and polymethyl methacrylate (the density is 1.1 g/cm) 3 ) 4%, dispersing agent 1%, thickening agent 2% and wetting agent 1%. The thickness of the composite diaphragm is 9 μm, the porosity of the composite diaphragm is 44%, the thickness of the mixed coating is 4 μm, and the D of the alumina 50 The particle diameter is 0.5 μm, and the specific surface area is 6.5m 2 The glass transition temperature of the intermediate aramid fiber of the mixed coating is 400 ℃ and the average grain diameter is 0.05 mu m.
The preparation method comprises the following steps:
(1) grinding and stirring aluminum oxide, polymethyl methacrylate, a sodium hydroxyethyl sulfonate wetting agent, a methyl cellulose thickener and deionized water, wherein the grinding speed is 1000rpm, and the stirring time is 10 hours, so as to obtain ceramic slurry;
(2) grinding meta-aramid, a sodium tripolyphosphate dispersing agent, polymethyl methacrylate and deionized water for 10 hours to obtain aramid pulp;
(3) and (3) mixing the ceramic slurry obtained in the step (1) and the aramid slurry obtained in the step (2), adding sodium hydroxide to adjust the pH value to obtain mixed slurry with the solid content of 35%, wherein the viscosity of the mixed slurry is 50cp, coating the mixed slurry on at least one side of a base film, and drying to obtain the composite diaphragm.
Example 5
This example provides a composite separator comprising a polyimide-based film (thickness 7 μm, porosity 65%, melting point 350 ℃) and a hybrid coating layer coated on at least one side of the polyimide-based film. The mixed coating comprises the following components in percentage by mass: 85% of alumina, 8.5% of meta-aramid and polymethyl methacrylate (the density is 1.3 g/cm) 3 )2 percent and 1 percent of dispersant2.5 percent of thickening agent and 1 percent of wetting agent. The thickness of the composite diaphragm is 13 μm, the porosity of the composite diaphragm is 46%, the thickness of the mixed coating is 6 μm, and the D of the alumina 50 The particle diameter is 1.5 μm, the specific surface area is 8.9m 2 The glass transition temperature of the middle aramid fiber of the mixed coating is 500 ℃, and the average grain diameter is 0.3 mu m.
The preparation method comprises the following steps:
(1) grinding and stirring alumina, polymethyl methacrylate, a sodium hydroxyethyl sulfonate wetting agent (molecular weight: 148.11, available from Guangzhou far-reaching New Material Co., Ltd.), a methyl cellulose thickener and deionized water, wherein the grinding rotation speed is 1000rpm, and the stirring time is 10 hours to obtain ceramic slurry;
(2) grinding meta-aramid, a sodium tripolyphosphate dispersing agent (molecular weight: 367.86, purchased from Jinan Shuihi chemical Co., Ltd.), polymethyl methacrylate and deionized water for 10 hours to obtain aramid pulp;
(3) and (3) mixing the ceramic slurry obtained in the step (1) and the aramid slurry obtained in the step (2), adding sodium hydroxide to adjust the pH value to obtain mixed slurry with the solid content of 40%, wherein the viscosity of the mixed slurry is 200cp, coating the mixed slurry on at least one side of the base membrane, and drying to obtain the composite diaphragm.
Example 6
The difference between the embodiment and the embodiment 1 is that the mass percent of the alumina in the mixed coating is 75 percent, the mass percent of the meta-aramid is 19.3 percent, and the rest is the same as the embodiment 1.
Example 7
The difference between the embodiment and the embodiment 1 is that the mass percentage of the alumina in the mixed coating is 90%, the mass percentage of the meta-aramid is 4.3%, and the rest is the same as that in the embodiment 1.
Example 8
This example is different from example 1 in that the alumina has an average particle diameter of 0.1 μm and a specific surface area of 12m 2 The rest was the same as in example 1.
Example 9
This example differs from example 1 in that the alumina has an average particle diameter of 2.5 μm and a specific surface area of 4m 2 The rest was the same as in example 1.
Example 10
This example is different from example 1 in that the meta-aramid has an average particle diameter of 0.01 μm, and the rest is the same as example 1.
Example 11
This example is different from example 1 in that the meta-aramid has an average particle diameter of 0.8 μm, and the rest is the same as example 1.
Example 12
This example differs from example 1 in that the glass transition temperature of the meta-aramid is 350 ℃, and is otherwise the same as example 1.
Example 13
This example differs from example 1 in that the glass transition temperature of the meta-aramid is 550 ℃, and the rest is the same as example 1.
Example 14
This example is different from example 1 in that the polymethyl methacrylate binder was replaced with polyvinylidene fluoride, and the other examples were the same as example 1.
Comparative example 1
The comparative example is different from example 1 in that meta-aramid is not added, the mass percentage of alumina in the mixed coating is 94.3%, and the rest is the same as example 1.
Comparative example 2
The comparative example is different from the example 1 in that alumina is not added, the mass percentage of the aramid fiber in the mixed coating is 94.3%, and the rest is the same as the example 1.
Application examples 1-14 and comparative application examples 1-2
The lithium ion batteries were prepared by using the composite separators provided in examples 1 to 14 and comparative examples 1 to 2, and the preparation method was as follows:
preparation of positive plate: lithium iron phosphate (LiFePO) with the particle size of 8 mu m 4 ) Acetylene black and PVDF were mixed in a mass ratio of 86:7: 7. Specifically, 0.05g of PVDF as a binder is accurately weighed in a weighing bottle, 10 drops of N-methylpyrrolidone (NMP) as a dispersant are added dropwise, the mixture is stirred for 1 hour in a heat collection type constant temperature heating magnetic stirrer (without heating), then 0.05g of acetylene black as a conductive agent is added, and the stirring is continued for 1 hour, then adding 0.6g of active material lithium iron phosphate, simultaneously adding 15 drops of polyvinylidene fluoride (NMP) solution, uniformly mixing, stirring for 12h on a magnetic stirrer to obtain a positive electrode material with certain viscosity and uniform stirring, adjusting the thickness of an automatic coating machine, controlling the total thickness after coating to be about 30 μm, uniformly coating the slurry on a flat aluminum foil by using a coating machine, drying for 7h at 80 ℃ in a common drying oven, taking out, cutting into circular pole pieces with certain diameter by using a punching machine, weighing, drying at 80 deg.C in a vacuum oven, and transferring to a glove box for use after 12 hr;
preparing a negative plate: mixing graphite, sodium carboxymethylcellulose and styrene butadiene rubber according to the mass ratio of 84:8: 8. Pouring the graphite mixed purified water into a vacuum stirrer, adding sodium carboxymethylcellulose, stirring, and completely dissolving; adding styrene butadiene rubber and deionized water, stirring for 60 minutes, uniformly adding the negative dry materials into a stirrer in four times, stirring for 3-5 hours in high-speed vacuum, and discharging for coating;
electrolyte solution: drying the lithium hexafluorophosphate LiPF 6 Dissolving in mixed solvent (ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate) with volume ratio of 1:1:1, and LiPF 6 The concentration of (2) is 1 mol/L.
Preparing a lithium ion battery: coating the prepared positive and negative electrode slurry on positive and negative current collectors, drying and welding tabs to obtain positive and negative electrode plates, then shearing the positive and negative electrode plates into positive and negative minimum electrode plates with a certain shape, isolating the positive and negative minimum electrode plates by cutting a composite diaphragm with a certain size in a winding or laminating mode, and winding the positive and negative minimum electrode plates into an electric core body; then, performing short circuit evaluation on the electric core body, and screening high-quality electric cores; then the materials are put into a battery shell, a battery cover is covered, and the opening is sealed by welding; and injecting electrolyte into the battery case, forming, sealing for the second time, baking by using the clamp and grading the volume to obtain the finished product of the soft package battery.
Test conditions
The composite separators provided in examples 1 to 14 and comparative examples 1 to 2 were subjected to a performance test by the following method:
(1) heat shrinkage ratio: the test sample dimensions were 10CM long and 10CM wide; heating by using an oven, wherein the test temperature is 200 ℃, and the test time is 1 hour;
(2) air permeability value: the test sample size was 5CM long and 5CM wide; testing the second time required for 100ml of gas to permeate the diaphragm by adopting a gas permeation tester;
(3) ionic conductivity: the test sample size was 18mm in diameter; punching sheets for standby; adopting an electrochemical workstation to test EIS;
(4) tensile strength: the size of a test sample is 10CM in length and 2CM in width, a universal testing machine is adopted, and the test speed is 100 m/min; the tensile force is 1 KN;
the lithium ion batteries provided in application examples 1-14 and comparative application examples 1-2 were tested for electrochemical performance by the following test methods:
(1) cycle performance: the test is carried out on a battery test system of an electrochemical workstation at the temperature of 25 ℃, the tested current density is 1C, and the charging and discharging voltage window is 2.75-4.2V.
(2) Rate capability: the test is carried out on a battery test system of an electrochemical workstation at the temperature of 25 ℃, the tested current density is 0.1C/1C/2C/3C, and the charging and discharging voltage window is 2.75-4.2V.
The results of the tests are shown in tables 1 and 2:
TABLE 1
Figure BDA0003576265220000161
Figure BDA0003576265220000171
TABLE 2
Figure BDA0003576265220000172
Figure BDA0003576265220000181
As can be seen from the data of tables 1 and 2, the composite separators provided in examples 1 to 5 of the present invention had a heat shrinkage of not more than 9%, a gas permeability of not more than 260s/100ml, an ion conductivity of not more than 5mS/cm, a puncture resistance strength of not less than 400gf, an elongation of not less than 90%, and a tensile strength of not less than 100Kgf/cm 2 。
Compared with the embodiment 1, the embodiment 6 and the embodiment 7 are the cases that the content of the ceramic and the aramid fiber is out of the range, and the comprehensive performance is not better than that of the embodiment 1; in the case that the particle size of the alumina is over the range, the particles with too small particle size are agglomerated to affect the air permeability of the diaphragm, and the particles with too large particle size are loose and are easy to generate short circuit in the examples 8 and 9; examples 10 and 11 are cases where the particle size of the meta-aramid is out of range, affecting breathability; examples 12 and 13 are cases where the glass transition temperature of the meta-aramid is out of range, affecting the heat resistance of the separator; example 14 replaces other binders to affect the tensile and impact resistance of the separator.
Comparative examples 1 and 2 are single-layer coated separators, which are inferior in thermal shrinkage or mechanical strength to the composite separator provided in example 1, compared to example 1.
As can be seen from the data in table 2, the capacity retention rate of the lithium ion batteries provided in application examples 1 to 5 is not less than 89.3% after being cycled 500 times at 0.1C, and the capacity retention rate of the lithium ion batteries is not less than 88.7% after being cycled 500 times at 1C.
Compared with example 1, the capacity retention rates of the single-layer coated separators of comparative application example 1 and comparative application example 2 at 0.1C and 1C are much lower than that of the lithium ion battery provided by application example 1, which shows that the composite separator provided by the invention can improve the electrochemical performance, mechanical property and heat-resistant stability of the battery.
The applicant states that the present invention is illustrated by the above examples of the process of the present invention, but the present invention is not limited to the above process steps, i.e. it is not meant that the present invention must rely on the above process steps to be carried out. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.

Claims (10)

1. The composite diaphragm is characterized by comprising a polyimide base film and a mixed coating at least coated on one side of the polyimide base film;
the mixed coating comprises the following components in percentage by mass: 80-85% of ceramic particles, 5-12% of aramid fiber, 2-4% of binder, 0.5-1% of dispersant, 0.5-2.5% of thickening agent and 0.1-1% of wetting agent.
2. The composite separator according to claim 1, wherein the thickness of the composite separator is 9 μ ι η to 13 μ ι η;
preferably, the porosity of the composite membrane is 44% -46%;
preferably, the thickness of the hybrid coating is 4 μm to 6 μm;
preferably, the thickness of the polyimide-based film is 5 μm to 7 μm;
preferably, the polyimide-based film has a porosity of 55% to 65%.
3. The composite separator of claim 1 or 2, wherein the ceramic particles in the hybrid coating comprise at least one of alumina, boehmite, or silica;
preferably, the average particle size of the ceramic particles in the hybrid coating is 0.5-1.5 μm;
preferably, the specific surface area of the ceramic particles in the mixed coating is 6.5-8.9m 2 /g；
Preferably, the aramid fiber in the hybrid coating comprises at least one of meta-aramid fiber or para-aramid fiber;
preferably, the average particle size of the aramid fiber in the mixed coating is 0.05-0.3 μm;
preferably, the glass transition temperature of the aramid fiber in the mixed coating is 400-500 ℃.
4. The composite separator of any of claims 1-3, wherein the binder in the hybrid coating is polymethylmethacrylate;
preferably, the density of the polymethyl methacrylate is 1.1 to 1.3g/cm 3 。
5. The composite separator according to any of claims 1-4, wherein the dispersant in the hybrid coating layer comprises any one or two of sodium tripolyphosphate, sodium hexametaphosphate, triethylhexyl phosphoric acid, sodium dodecyl sulfate, methyl amyl alcohol, polyacrylamide or fatty acid polyglycol ester, preferably polyacrylamide and/or fatty acid polyglycol ester.
6. The composite separator of any of claims 1-5, wherein the thickener in the hybrid coating layer comprises any one or two of arabic, sodium carboxymethylcellulose, propylene glycol alginate, methylcellulose, sodium starch phosphate, sodium polyacrylate, polyoxyethylene, polyvinylpyrrolidone, ethylene methyl ether-decadiene copolymer, methyl acrylate-decadiene copolymer, or polyurethane, preferably sodium carboxymethylcellulose;
preferably, the wetting agent in the mixed coating comprises any one or two of polyethylene glycol, tween-80, vaseline, polyether modified siloxane copolymer, waterborne polyurethane, polyoxyethylene octylphenol ether, polyoxyethylene castor oil ether or sodium isethionate, and preferably polyethylene glycol 200 and/or polyether modified siloxane copolymer;
preferably, the mixed coating also comprises a pH regulator;
preferably, the pH adjusting agent is sodium hydroxide.
7. A method of making the composite separator of any one of claims 1-6, comprising the steps of:
(1) mixing ceramic particles, a binder, a wetting agent, a thickening agent and a solvent to obtain ceramic slurry;
(2) mixing aramid fiber, a dispersing agent, a binder and a solvent to obtain aramid fiber slurry;
(3) and (3) mixing the ceramic slurry obtained in the step (1) and the aramid slurry obtained in the step (2), adding a pH regulator to obtain a mixed slurry, coating the mixed slurry on at least one side of the base film, and drying to obtain the composite diaphragm.
8. The method according to claim 7, wherein the solvent in step (1) is deionized water;
preferably, the mixing in step (1) is carried out under milling and stirring;
preferably, the rotation speed of the grinding is 500-;
preferably, the stirring time is 4-15 h;
preferably, the solvent in step (2) is deionized water;
preferably, the mixing in step (2) is carried out under milling;
preferably, the grinding time is 4-15 h;
preferably, the solid content of the mixed slurry in the step (3) is 35-40%;
preferably, the viscosity of the mixed slurry in the step (3) is 50-200 cp.
9. The method according to claim 7 or 8, wherein the coating in step (3) is spot coating.
10. A lithium ion battery, which is characterized by comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the separator is the composite separator according to any one of claims 1 to 6.
CN202210345179.9A 2022-03-31 2022-03-31 Composite diaphragm, preparation method thereof and lithium ion battery Withdrawn CN114865225A (en)

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CN114243217A (en) * 2022-02-24 2022-03-25 湖南中锂新材料科技有限公司 Lithium ion battery composite diaphragm and preparation method thereof

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CN114243217A (en) * 2022-02-24 2022-03-25 湖南中锂新材料科技有限公司 Lithium ion battery composite diaphragm and preparation method thereof

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CN115347325A (en) * 2022-09-26 2022-11-15 惠州亿纬锂能股份有限公司 Composite diaphragm, preparation method thereof and sodium ion battery
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